Method and apparatus for tomographic touch imaging and interactive system using same

ABSTRACT

A touch screen in the form of a panel is capable of conducting signals and a tomograph including signal flow ports is positioned adjacent the panel with the signal flow ports arrayed around the border of the panel at discrete locations. Signals are introduced into the panel to pass from each discrete border location to a plurality of other discrete border locations for being detected and tomographically processed to determine if any change occurred to signals due to the panel being touched during signal passage through the panel, and therefrom determine any local area on the panel where a change occurred. The tomograph computes and outputs a signal indicative of a panel touch and location, which can be shown on a display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority and benefit of previously filedArgentinean Patent Application No. 20070105651 filed on Dec. 17, 2007,in the name of Victor Manuel Suarez Rovere, which is here incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for tomographic touchimaging sensor and interactive system using same. More particularly, theinvention relates to a method and apparatus for touch sensitive devicesfor computing systems or for controlling actions of associated devicesor equipment, and still more particularly, to devices that detect and/orprocess simultaneously multiple touch interactions (by fingers or otherobjects) at distinct locations on a touch-sensitive surface.

2. Prior Related Art

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, touch panels, joysticks, touch screens and the like. Touchscreens, in particular, are becoming increasingly popular because of theease and versatility of operation, as well as, their declining price.Touch screens can include a touch panel, which can be a clear panel witha touch-sensitive surface. The touch panel can be positioned in front ofa display screen so that the touch-sensitive surface covers the viewablearea of the display screen. Touch screens can allow a user to makeselections and move a cursor by simply touching the display screen via afinger or stylus. In general, the touch screen can recognize the touchand position of the touch on the display screen, and the computingsystem can interpret the touch and thereafter perform an action based onthe touch event.

One limitation of many conventional touch panel technologies is thatthey are only capable of reporting a single point or touch event, evenwhen multiple objects simultaneously come into contact with the sensingsurface. That is, they lack the ability to track multiple points ofcontact at the same time. Thus, even when two points are touched, theseconventional devices can only identify a single location, which istypically the average between the two contacts (e.g. a conventionaltouchpad on a notebook computer provides such functionality). Thissingle-point identification is a function of the way these devicesprovide a value representative of the touch point, which is generally byproviding an average resistance or capacitance value.

Another limitation of most touch panels is that, besides being incapableof reporting a plurality of touch points that occurs simultaneously, isthat they provide information about just touch coordinates. Most knowntouch panels cannot provide a complete representation of the details ofall shapes contacting the panel, because the methods of detection ofteninclude just triangulation of touch points. Thus, a need exists forproviding a better and fuller representation of touch interactions. Thepresent invention proposes to provide a method and apparatus forachieving, for example, by providing a pixilated image representative ofall the touch areas and their shapes. This ability of providing a fullrepresentation of all touch interactions is sometimes called“true-touch”.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of my invention to provide amethod and apparatus for tomographic touch imaging and interactivesystem using same, especially for computing systems but also usable tocontrol actions of other devices, and still more particularly, todevices that detect and/or process simultaneously multiple touchinteractions (by fingers or other objects) at distinct locations on atouch-sensitive surface. The foregoing is accomplished by combining atouch panel with a tomograph in a unique way, and by using thiscombination as a touch imaging sensor and/or as an interactive system ina computer system.

The present invention applies techniques from tomography field ofscience, but instead of using it for medical purposes, the tomographictechniques are used for making a computer input device. Specifically,the input device is a touch device capable of multi-touch operations,oriented to control the forthcoming new generation of softwareapplications that propose a new paradigm for Human Computer Interaction.

Since tomography is used to determine inner information from the bordersof a panel, and because invisible signals are used, it is possible tomake a transparent touch panel with almost perfect light transmissionproperties. The transparent properties make the touch sensor useful towork with a display, as a touch screen. Other such input devices need toput complex elements on a panel that obstruct vision. As these othersuch input devices need to have at least some transparency, but not100%, this requirement makes it difficult to manufacture, affectingcosts.

The present invention can be implemented with a very clear andhomogeneous material, like a simple sheet of acrylic. Also, because thepanel can be very thin, a slim and small system including a flat displaycan be made, thus enabling the system to be portable.

Several objects and advantages of my invention are listed as follows.

-   a) To provide a device that is sensitive to touch and able to detect    objects when they are making a subtle pressure. If the object    touching is a finger of an user the invention can provide a tactile    feedback. This is in contrast to proximity sensors which can be    activated when the user isn't touching anything.-   b) To provide a touch sensitive device that can provide a digital    representation of nearly all areas where there is a touch    interaction available. This is in contrast to devices that provide    location information of just a few touch interactions    simultaneously.-   c) To provide a touch sensitive device that can be thin, thus having    a large relative surface area with respect to volume.-   d) To provide a touch sensitive device that can have a transparent    touch panel so that it can include a display visible through the    panel.-   e) To provide a touch sensitive device that can be interactive by    providing output information related to touch interactions.-   f) To provide a thin touch sensitive device that can be flat, or    non-planar (e.g. domed) in 3-dimensional space.-   g) To provide, in some embodiments, a touch sensitive device that    can detect a zero-pressure contact.-   h) To provide, in some embodiments, a touch sensitive device that    can discriminate regarding more than one level of pressure on    possible different touch interactions that occurs simultaneously.-   i) To provide, in some embodiments, a touch sensitive device that    can be robust to some external unwanted interfering signals.-   j) To provide, in some embodiments, a touch sensitive device that    can have a transparent touch area of quite low absorption with    respect to visible light, useful to make the power requirements of a    possibly attached display less demanding.-   k) To provide, in some embodiments, a touch sensitive device that    can be constructed with elements relatively easy to manufacture.

Further object and advantages of my invention will become apparent fromthe following detailed description of preferred embodiments of theinvention when taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show, respectively, a top view of the basic tomographictouch device of the present invention, and a cross sectional view takenalong line A-A of FIG. 1A.

FIG. 1C shows selected imaginary or notional regions or areas of thetouch panel shown in FIGS. 1A and 1B illustrating where touchinteractions may occur or be estimated.

FIG. 2 shows an annular shape representing a particular “test” touchinteraction made on a rectangular touch panel.

FIG. 3 shows components of a typical tomograph as used in the presentinvention.

FIG. 4A shows one simple way of defining geometries for the tomographyapparatus according to the invention.

FIG. 4B shows a very useful way of defining geometries for thetomograph.

FIGS. 5A and 5B show, respectively, a top plan view and a crosssectional view of a touch device taken along line B-B of FIG. 5A thatincludes a display and a computer as part of an interactive systemaccording to the present invention.

FIGS. 6A to 6B show, respectively, a top view of a similar touch devicecombined with an electrical impedance tomograph and a cross sectionalview taken along line C-C of FIG. 6A.

FIG. 7 shows an embodiment of the present invention that uses just anair gap to optically couple emitters and detectors to a panel, and theeffect of signal reflection on a panel's edge.

FIG. 8 shows two typical emission patterns and its associated detectors,and the signal alteration level measured on each detector after passingthrough an annular phantom.

FIG. 9 illustrates a flowchart of the operation of an embodiment of thetouch device as part of an interactive system.

FIG. 10A illustrates a flow chart of the tomographic touch sensoroperation.

FIG. 10B illustrates a flow chart of the tomographic touch screenoperation.

FIG. 11 illustrates a flow chart of the interactive system using atomographic touch sensor, a data processing element, and an outputdevice.

FIG. 12 illustrates a flow chart showing an example embodiment for theacquisition of a tomogram representative of touch interactions.

FIG. 13 illustrates a flow chart showing an example embodiment for theacquisition of an unreconstructed tomogram representative of touchinteractions.

FIG. 14 illustrates a flow chart showing an example embodiment for thereconstructed tomogram calculation.

FIG. 15 illustrates a flow chart showing an example embodiment for thedefinition of parameters for tomogram acquisition.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the drawings, and particularly to the embodiment of thepresent invention, a touch device is illustrated in FIG. 1A (top view)and FIG. 1B (cross sectional view). The touch device, as shown, consistsof a thin, flat, circular panel 10 of light conductive material, such asa suitable plastic material known for this purpose. The panel 10, due toits properties is adapted to conduct signals, introduced into theborders of the panel, through the panel. The panel can be opaque ortransparent and can be rigid or flexible. The panel can also beresilient and/or compressible. The signals may be any radiation or waveenergy that can pass through the panel from border to border or edge toedge including without limitation, light waves in the visible orinfra-red or ultraviolet regions of the spectrum, electrical energy,electromagnetic or magnetic energy, or sonic and ultrasonic energy orvibration energy. In the following description, light passing throughthe panel will be described as a preferred embodiment. The light signals20 are introduced through the edge or border 22 of the panel 10, asshown in FIG. 1B. The shape of the panel 10 is not limited to anyparticular shape and may be irregular or regular, such as, circular,elliptical, square, rectangular or polygonal. The panel has a refractionindex greater than air so it can act as a waveguide by the effect of TIR(Total Internal Reflection). Touch interactions at discrete locations onthe panel surface 12 can interfere with, disrupt or frustrate the TIReffect so that a portion of the signal (light) is lost by escaping thewaveguide of the panel. This is indicated in FIG. 1B by the referencenumeral 14 showing the light exiting form the panel, i.e. light loss.Thus, the light conductive properties of the panel are altered in thoseplaces where the touch interactions occurs, as indicated by referencenumeral 16 in FIG. 1A.

Surrounding the conductive panel 10, there is an optical tomograph 30.In the context of the present invention, “tomograph” means, as usuallydefined, a device that can image from the borders. The tomograph iscontrolled to emit light signals 20 by light emitters 34, through signalflow ports, which also detects light signals by detectors 32.

The term “signal flow port” refers to both emitters and receivers(detectors), and the signal flow port physically acts either as emitteror receiver. For example, an electrode in the electrical part of theembodiment can be a unique device that could serve both purposes emitterand/or receiver. Also an optoelectronic device like a LED can be used asa detector, although with less performance. So a signal flow port hereisn't anything material and thus, isn't either an element that can housean emitter or detector. In the context of this invention, a signal flowport is a term used to refer interchangeably to an emitter, or to adetector, or to a device that may accomplish both roles. Thus, the porthouses an emitter and/or detector and may be virtual or real.

The signal flow ports (emitters and detectors) are positioned at theedge 22 of the panel 10. The light signals 20 introduced into the panel10 by emitters 34 at their associated signal flow ports penetrate orpass through the panel 10, in the manner described, and are detected bydetectors 32 at their associated signal flow ports after circulating orpassing through the panel 10. The tomograph 30 generates a tomogramrepresentative of the panel conductivity, which is a two dimensionalrepresentation of the calculated or estimated conductivity on manyimaginary or notional regions 40 defined on the panel surface 12, asshown by the array on FIG. 1C (top view). The resulting tomogram is thusa calculation or an estimative representation of the touch interactions,including its shapes and details. The tomogram may be calculated torepresent the conductivity change produced by touch interactions, bycomparing it with the conductive properties of the panel when no touchinteractions occur. The resulting tomogram can be provided as digitalinformation aimed to control or operate a digital device. The digitaldevice may include an output device, such as a display, and a processingelement to transform the tomogram and provide output to a user asfeedback of touch interactions, thus forming an interactive device.

An exemplary shape 50 of an interesting and quite challenging touchinteraction is shown on FIG. 2 (top view). Shown is an annular shapethat could be an approximation of the contact area produced by the palmof a hand touching a rectangular touch panel. As will be appreciated,the resulting tomograph can represent any complex figure or shapedepending on the touching interactions. As a parallelism with medicalX-ray tomography, the annular shape shown could be an approximation ofthe cross section of a hollow bone. It will be appreciated that CT orcomputerized tomography is a well known technology and is understood bythose of ordinary skill in the art.

The tomograph 30 of the touch device as illustrated on FIG. 3 maytypically comprise a set of signal flow ports 18. Each signal port maybe an emitter and/or a detector for the signals, where the signal flowsthrough the port. An emitter 34 is typically an electronic device, forexample an IR LED (Infrared Light Emitting Diode) or other lightemitting device. A detector 32 is typically an electronic device, suchas a phototransistor, photodiode, Charge Coupled Device (CCD) and otherlike devices. The signal flow ports are typically located around theperiphery or perimeter (edges 22) of the conductive panel 10 and spacedapart, usually at regular intervals. The emitters 34 are opticallycoupled to the panel, in a way that at least a portion of the emittedsignal penetrates the conductive panel 10 and circulates or passesthrough by effect of TIR. The detectors 32 are optically coupled to thepanel 10 in a way that each detector 32 receives the emission signals 20emanating from one or more of the emitters 34 via signal flow ports 18.The ports may be coupled to the conductive panel by via a couplingobject that may be optical glue, or just direct contact, or a waveguidelike an optical fiber, a diffuser or just an air gap, or by any otherknown means provided the light from the emitters 34 is introducedproperly into the panel 10 and the light is detected by the detectors32. Although by using an air gap 92, see FIG. 7, total reflections couldoccur on the border of a polished panel, before reaching a detectorclose to the point of reflection, as shown in FIG. 7, anyways thereflected signal may approach another detector, thus tomographicreconstruction still could be accomplished.

The tomograph 30 also includes an emission pattern controller 60operatively coupled to each emitter 34, for example, using anyconventional set of communication channels 62, shown in FIG. 3 as wires.The tomograph 30 further includes a signal sampler 64 operativelycoupled to each detector 34. Also the tomograph 30 includes a dataprocessor 66 operatively coupled to the pattern controller 60, and tothe signal sampler 64.

The emission pattern controller 60 can energize, upon requirement oraccording to any predetermined program, any desired combination or setof said emitters 34. Each emitter 34 can be energized at any desiredemission level of at least two possible values. The configuration of aset of emitters and its levels defines an emission pattern. Arepresentative emission pattern, according to the invention, can be tohave one determinate or preselected emitter 34 active while leaving therest inactive, and then serially process through the emitters 34, one ata time.

The signal sampler 64 can measure, upon requirement or according to anypredetermined program, the signal level received on each detector 32. Arepresentative signal sampler 64, according to the invention, can haveone or more Analog to Digital Converters (ADC) and also may have one ormore analog and/or digital multiplexers.

The data processor 66 can be incorporated in any known computer system,and is adapted to command the emission pattern controller 60 to energizethe emitters 34 using a desired sequence of patterns. Also the emissionpattern controller 60 and/or signal sampler 64 may function based on adeterminate or preselected program, without being commanded by the dataprocessor, for example a digital logic circuit.

By operating the emission pattern controller 60 and the signal sampler64, an unreconstructed tomograph can be acquired.

To operate emission controller 60, a set of emission patterns has to bedefined, for example, a sequence of patterns may be to activate, in turnor serially, different emitters 34. Each emission pattern is active atdifferent times, forming a sequence. While each emission pattern is ineffect, an associated set of detectors 32 have to be defined to measurethe effects of the active emissions. Then, the data processor 66acquires from the signal sampler 64, the measured values from theassociated set of detectors 32, the set being typically all or asubstantial subset of the detector 32. The measured values form part ofthe unreconstructed tomogram. Thus after applying all emission patternsand obtaining measurements from the detectors, the unreconstructedtomogram is obtained. An example of two emission patterns, itsassociated detectors, and a representation of the signal alterations,shown in graph of FIG. 8, received for the annular phantom, is shownalso in FIG. 4B.

The data processor 66 may be a microcontroller, microprocessor, FPGA,ASIC or special purpose electronic circuit or even part of a completecomputer system. Although it may be desirable for the data processor 66to include a data memory containing a computer program, it is possibleto practice the invention performing most computations with just adigital logic circuit. For example, a tomographic reconstructioncalculation, as known in the art, can be executed just with anintegrated circuit. That integrated circuit can lack a specific“memory”, because computation can be hardwired. The inventioncontemplates a model using a programmable logic circuit (FPGA) that hasa memory, but without any “computer program” as such stored in thememory.

In a typical embodiment, the data processor 66 commands the emissionpattern controller 60 to activate one determinate emitter 34, then,acquires measurements from all detectors 32, then, repeating these stepsserially for the rest of the emitters 34, one by one. Thus, if thenumber of emitters 34 is N_(e) and the number of detector ports isN_(d), a vector of N_(e) by N_(d) elements is acquired. One can callthis vector the projection vector, or one can call it a measurementsvector, or just “b”. This acquired vector, not to be confused with amatrix, is sometimes called in the context of Computer Tomography (CT)the “unreconstructed tomogram” or sometimes “sinogram”.

Having the unreconstructed tomogram with N_(e) by N_(d) potentiallyindependent values, the amount of available information to makereconstruction can be thus in quadratic relation with respect to numberof signal flow ports. So the number of potentially independentlyrecognized touch interactions regions can be in accordance to thatquadratic relation, and not in linear relation with respect to number ofemitters 34 or detectors 32. Thus, that number of potentiallydiscriminated regions can be quite large or big. Hence, the foregoing isa sample of the potential of the present invention of being able todiscriminate not just a few simultaneous touch coordinates, but many.

Having the unreconstructed tomogram, a reconstructed tomogram can becalculated by the use of a Tomographic Reconstruction algorithm. Thereconstructed tomogram, or just tomogram, is the representation of thefeatures of the tomographed “phantoms”, a phantom being a particular“test” or “active” touch interaction.

In a tomographic reconstruction algorithm, a linear or nonlinear modelof the tomographic system may be used to transform the unreconstructedtomogram. If a linear model is chosen, the system may be modeled bymatrix equations and solved by linear matrix operations in a knownmanner.

A typical equation used to model tomographic systems is Ax=b, where Acorresponds to the “system matrix”, as is sometimes called, xcorresponds to the reconstructed tomogram and is a vector thatrepresents the regions conductivity values, not to be confused with amatrix just because regions are usually a grid. The variable b is theunreconstructed tomogram, a vector containing the measured projectionvalues reaching the detectors 32 for each emission pattern. The systemmatrix, in the context of CT, represents the transformation that thetypical linear tomograph system accomplishes to generate the projectiondata. A typical linear tomograph thus works by transforming b into xtaking into account matrix A as a transformation operator.

To be able to calculate a two-dimensional tomogram adequately, one needsto have defined appropriate locations to each emitter 34 and detector32, which are typically surrounding the panel 10 on its edge(s). Also,one needs to define imaginary or notional locations and shapes of a setor array of regions 40 on the surface 22 of the panel 10, where anestimation of conductivity is going to be calculated. The regions 40 aresometimes called “reconstruction regions”. In a typical embodiment, theregions 40 are rectangular and are disposed next to each other in anappropriate imaginary or notional grid of pixels.

Also, to be able to calculate an adequate tomogram, the regions have tobe geometrically defined in a way that each region is affected by morethan two non-parallel line integrals; each line integral being definedas the path of an actually measured signal between a determined pair ofemitter 34 and detector 32. This is to accomplish, for each region,adequate “angle density” as is usually called. In a diffusion tomographthe concept of line integrals may be geometrically not similar to aline, but to a sort of “field” as shown on FIG. 6A.

A determinate signal corresponding to a line integral may be altered inmore than one point of its path without being substantially obstructedby a single touch, as depicted in FIG. 1B. That physical property of thepanel with respect to conduction of signals is an important factordetermining ability of permitting adequate tomographic reconstruction.For example if the touch interaction substantially would obstruct thesignal, and another touch in other part of the signal path wouldn'tfurther alter the signal, the annular phantom as shown on FIG. 2 wouldbe easily confused, by that hypothetic system, with a filled circle,because that system would be unable to adequately estimate the interiorproperties of the phantom. That property of possible successivealterations of the signal along a line integral, configures an “integralfunction” as sometimes is called. Also, to be able to adequately measurethe possible effects of touches over an emitted signal, measurements bythe use of analog to digital conversion techniques are important.

Those skilled in the art will understand that the requirements of highangle density for each region and existence of an integral function todo tomographic reconstruction has support in the Projection SliceTheorem, which is related to the Radon Transform. Basically, theprojection-slice theorem tells us that if one had an infinite number ofone-dimensional projections of an object taken at an infinite number ofangles, one could perfectly reconstruct the original object, f(x,y).Note the need of multiple angles (as much as possible in anon-theoretical device) and the need of “projection” (ie. integrationdata) along the line. However, the present invention is not limited bythis theorem.

It's well known that a finger interacting with a waveguide like in thepresented embodiments makes better and broader optical contact as morepressure is applied. This effect is because, together with other causes,the skin on the fingerprints gets more deformed, so the average contactarea per unit area and thus, average conductivity gets altered in ahigher level. This higher change of conductivity could be interpreted asmore pressure and used to take distinctive actions. For example an iconof a user interface can be selected with a light pressure but activatedwith more pressure.

Also, as in any measurement instrument, repeated measurements over timecan be done to have a time-varying measurement, so taking a series oftomographs over time is useful to determine how touch interactionschanges over time, and that information may be used to detect touchevents or gestures, with algorithms well known in the art.

Another embodiment of the touch device, as illustrated in FIGS. 5A and5B (top plan and cross sectional view, respectively) may include adisplay 70 beneath the touch panel 10 preferably transparent, to form atouch screen. The touch panel 10 is bent at its edges and the signalflow ports incorporating the emitters 34 and the detectors 32 arearrayed around the bent down perimeter of the device. Light rays 20 passthrough the touch screen as described. The touch screen may makeavailable the information related to touch interactions generated by thetomograph, to be interpreted by a digital system, and then the digitalsystem may control the display to show information related to the touchinteractions, to be seen through the clear panel. The panel 10 could beconvexly curved, and that curved panel could serve to house the display70 and also to permit the ports to be easily put or mounted on asubstrate like a printed circuit board (PCB).

Another embodiment of the touch device, as illustrated on FIG. 5B, mayinclude the output device 70 operatively coupled to the data processor66 or to an alternative data processor to form an interactive system.The interactive system transforms the tomogram informationrepresentative of touch interactions produced by a user, intoinformation to be represented in the output device 70 as feedback totouch interactions. Touch user interactions in the interactive systemmay be used to modify the state of the software running in theprocessor, and when the software reflects its modified state in anoutput device, such as a display, the user receives feedback related tothe touch interactions. The typical embodiment of the interactive systemmay be a cell phone including the touch sensitive area and displayingthe images on its user interface.

The transformation of the information representative of touchinteractions into information for the output device may be of the typecommonly used in Graphical User Interfaces (GUI). For example, thetransformation could be to show an icon on the display with analternative color when a touch interaction event is detected on an areainside the icon, so a user can have the sensation of touching the icon.

The output device 70 may typically be a display such as a Liquid CrystalDisplay (LCD). A device with a display behind a transparent panel toform an interactive system is one of the main objectives of theinvention. However, the touch sensor could be used without a display,for example, just to generate sounds.

The tomograph representative of regions where touch interactions occurmay be like a pixilated image representing the conductivity on eachregion, but an event based GUI may be designed to just acceptcoordinates of touch interactions or more complex gestures instead oflevel of activity on determinate regions. So an algorithm to translateactivity on each region to coordinates of touch interactions or gesturesis useful and contemplated by the invention. The algorithm fordetermination of touch events often called “Blob Detection and Tracking”and is well known in the art. It is used by some systems that calculateand track touch locations by first using computer vision over an imageof the touch regions, and using the image captured with a video camera.

In another embodiment of the touch device according to FIG. 6A (topview) a conductive panel 80 may be rendered electrically conductiveusing the signal flow ports, which can be simple electrodes 82, and thesignals 84 may be electric currents. The electrically conductive panel80 may be of a material as shown in U.S. Pat. No. 4,448,837, which isconductive and transparent. Another way to implement the electricallyconductive panel 80 is by depositing a thin film of transparentconductive material over a non-conductive transparent substrate, so thetouch of a finger makes some part of the currents normally circulatingon the panel, to circulate through the skin thus lowering the resistanceon the contact points. A display is mounted beneath the touch screen aspreviously described.

In another embodiment of the touch device the panel may be of a materialacting as a dielectric, and the tomograph may be a CapacitanceTomograph, where the touch of a finger or other object can alter thedielectric properties of the panel.

In another embodiment of the touch device the panel may be of a materialacting as a vibration conducting medium, and the tomograph may haveacoustic or piezoelectric transducers as ports, in a similar way as anultrasonic tomograph for pregnancy is implemented. The acousticimpedance of the panel can be altered by the touch of a finger or otherobject.

Operation

The operation of the touch screen device included in an embodiment of aninteractive device (the method of the invention) is shown in the flowchart of FIG. 9 and is described as follows.

Steps S1 to S7 carried out as described in the blocks of FIG. 9 defineand calculate parameters for posterior tomograph acquisition andreconstruction. These parameters can be calculated during theinteractive operation of the system or device, or optionally theinformation can be calculated and stored in memory for later recall.

Steps S8 to S22 carried out as described in the blocks of FIG. 9 are agroup of steps that repeats indefinitely while a user is interactingwith the interactive device. Steps S9 to S14 obtain an unreconstructedtomogram; steps S15 to S17 calculate a reconstructed tomogramrepresentative of detected or sensed touch interactions. This is carriedout by a suitable algorithm as detailed in the blocks of FIG. 9 forachieving tomographic reconstruction, but other well-known algorithmsfor tomographic reconstruction can be used. Some of these algorithms arewell explained in the book “Principles of Computerized TomographicImaging” by Kak and Slaney, available on the web.

Step S18 to S22 are carried out as described in the blocks in FIG. 9 forprocessing touch information to control an application and providefeedback to the user.

Step S1 is for defining positions and shapes of the imaginary ornotional reconstruction regions over the sensitive surface. The regionsforms typically a pixilated grid but each region can have its own shape,that can be polygonal, or inclusive defining a surface of more than onedisjoint shape.

Step S2 is for defining the set of emission and detector ports to beinvolved in unreconstructed tomogram acquisition, and also for selectingits positions. The port positions may be typically the surroundings ofthe sensitive panel, for example alternating an emitter with a detectorat regular intervals. Also, the positions may be near just some portionsof the panel's surroundings, for example on just a subset of edges of apolygonal panel. Where there are not ports, the panel may havereflective materials so signals can bounce there (be reflected) andreach other ports.

FIG. 4A (top view) is a quite unuseful way of define regions 40 and port18 locations. If all emitter 34 ports 18 are disposed just on the leftof a square panel 10, all detector 32 ports 16 disposed just on theright, measurements done along just horizontal paths, and reconstructionregions 40 are all vertical rectangles that span from top to bottom, thetwo dimensional reconstruction that could be done would not produce veryinteresting results. This example shows that some awkward ways ofdefining geometries lead to difficulties on tomographic reconstruction.Anyways, the most intuitive and easily defined geometries lead to goodresults. For example, as shown in FIG. 4B simply disposing alternatingemitter and detector ports around the panel, measuring from asubstantial subset of the possible emitter-detector pairs, and selectinga pixilated grid for the reconstruction regions in an amount inquadratic relation with number of emitters and detectors, good resultscan be achieved.

Step S3 is for defining a sequence of emission patterns, where thesequence typically contains a linear independent set of emissionpatterns, for example, the activation in sequence of just one emitter.Another set of patterns may include patterns interpreted as a matrixthat has a substantially high rank so different emission patterns can bediscriminated. Matrix rank is well known to those of ordinary skill inthe art. Another example of patterns can be Code Sequences as normallyused for CDMA, a well known technique for multiplexing. The objective isto permit multiplexing and adequate discrimination of the differentpatterns.

Step S4 is for defining for each emission pattern a set of associateddetector ports. Once an emission pattern is active, the signal reaches aset of detector ports and some of them are selected for measurement. Theset of ports associated with an emission pattern may be selected takinginto account the level of the signal normally received.

Step S5 is for taking a reference unreconstructed tomogram that will beused as reference to calculate the differences on conductivity when anytouch is occurring. The panel has default conductivity when no touch isaffecting its conductivity, and the measurements are for determining thechanges produced by touch interactions.

Step S6 is for calculating the system matrix A, assuming a linear modelof the tomographic system. A possible way of calculating the systemmatrix to be further used to calculate the tomogram may be by making Xan identity matrix, on equation AX=B, being B a matrix of measurements,a set of unreconstructed tomogram acquisition. So if X is the identity,thus A=B, thus the way of calculating A may be to touch in sequence eachreconstruction region with corresponding shape and “unit pressure”, andmeasuring in each touch step the projection, so to construct B, and thusthis set of measurement results in the system matrix A. This procedure,as explained above, will be readily evident to a person of ordinaryskill in the art.

Step S7 is for calculating its pseudoinverse A′ by using a TruncatedSingular Value Decomposition (TSVD) algorithm. A typical algorithm forpseudoinverse calculation is provided by the function pinv of the MATLABsoftware from MathWorks. The parameter that controls the truncation maybe used to adjust the results provided by the reconstruction algorithm,for example to make a better estimation of the conductivity values byreducing resulting reconstruction noise by the use of that truncationparameter. A way of estimating the truncation parameter may be tosimulate the system with respect to its noise performance, andoptimizing the parameter trying to minimize the noise figure.

The definition of parameters for tomographic reconstruction, thatincludes the definition of regions, position of ports, and sequence ofemission patterns with its associated detectors, needs to be selected ina way to permit adequate reconstruction. A way of evaluating suitabilityof parameters, is by calculating the associated system matrix A,assuming a linear model of the tomographic problem, and then evaluatingcharacteristics of the matrix A. For example, a criterion could be toevaluate if the matrix rank is close to number of defined regions, andwith a condition number that characterizes a “well-conditioned” problem.If after evaluating suitability of tomographic parameters, they don'tmeet the defined criteria, the parameters can be redefined until thecriteria are met. For example, less and bigger regions may be defined.Conditions number, rank, and matrix conditioning are concepts wellunderstood to those skilled in the art.

Step S8 represents the actions of a user that perform control operationsthrough one or more touch interactions that can occur simultaneouslyover the sensitive surface.

Step S9 is for initializing a vector b for holding the posterioracquired unreconstructed tomograph.

Step S10 is for energizing emitter ports by configuring the patterncontroller with an emission pattern. In each step of the loop, eachemission pattern is selected, in sequence, from the set of definedemission patterns and applied.

Step S11 is for measuring the signal levels reaching the set of detectorports associated with the active emission pattern. To measure signallevels having some rejection to possible interfering signals, forexample external light on the optical embodiment, a double reading canbe done. For example, the signal levels reaching detectors with allemitters off can be subtracted from the value measured when emissionpattern is active.

An embodiment can discard some of the acquired values with a criterion,or just not measure the value. For example, emitting from a determinateemitter and measuring from a detector in close proximity, may be oflittle use. Other criteria to discard measurements may includediscarding emitter-detector combinations that involves a weak signalbetween them, because, for example, their relative angle of incidence.Most emitters and receivers respond weakly to signals at high angleswith respect to the perpendicular. Also, the measured values can beweighted by associating weighting factors with each measured value,being that operation useful to reduce overall reconstruction noise.

Step S12 is for subtracting to this value, the corresponding referencevalues taken from vector b0. So when no touch is active, the resultingvalue will be zero plus the possible measurement noise. And in Step 13,the obtained values are appended to the vector b. As shown on Step S14,the steps from S10 to S13 are repeated until unreconstructed tomographis completely acquired.

Step S15 is for preprocessing the unreconstructed tomogram, for exampleto linearize it by applying for example a nonlinear operation, in asimilar way that most X-ray tomography devices first apply a logarithmto linearize the cumulative effect of successive attenuations thattissue imposes to X-rays. Step S16 is for calculating the reconstructedtomograph x by solving the equation x=A′b, where A′ is the pseudoinverseof system matrix and b is the unreconstructed tomograph. Step S17 is forpost processing the reconstructed tomogram, for example with a noisegate that assign zero to values that are below some threshold. Thethreshold can be set just above normal peak noise values.

Step S18 is for recognizing touch interactions taking into account thereconstructed tomogram and generate touch events. To recognize events, aset of previously acquired tomograms may be also used. Algorithms ofrecognition of touch events and gestures are well known in the art andare sometimes called “blob tracking and detection”, and may be based onalgorithms such as the Watershed algorithm. The kind of eventsrecognized can be a new touch appearing, a touch disappearing, anexisting touch moving, or other gestures. A gesture can be a “pinch”gesture that is produced by touching the panel in two locations, andseparating apart the fingers. That pinch gesture can be used for exampleto control the zoom factor in a map application. A touch event can beassociated with a coordinate that can have more resolution than theprovided by the reconstructed tomogram. A set of values around an areawhere the touch is occurring, can be processed to obtain a sub-pixelcoordinate. For example, having a 3×3 pixels area, the coordinate ofeach pixel center on that area can be averaged by weighting itscoordinate with the value associated with each pixel, obtaining acoordinate similar to each pixel but with sub-pixel resolution.

Alternatively, another embodiment of the touch device operations mayskip touch the events detection and generation, transforming thereconstructed tomogram by DSP algorithms or other methods to control theoutput device. For example the output device may be a sound generationdevice. The application to be controller may be a synthesizer, usingtouch interactions to alter synthesizer parameters. As an example,interactions on the horizontal axis may be mapped to pitch andinteractions on the vertical axis, to harmonics levels, thus forming amulti spectral instrument.

Step S19 is for modifying the state of a user interface program inresponse to the touch events. For example if the user interface has amodel of a virtual button, that button state becomes active if a touchinteraction is detected on the area within the virtual button perimeter.

Step S20 is for generating the output information representative of thealtered state of the UI program. For example, in the virtual buttoncase, the output information is one that maps to different colorsaccording to the button activation state.

Step S21 is for showing output information on the display adapted tothat information through a transparent implementation of the touchsensitive panel.

Finally, the output of Step 21 is passed to Step 22, which is the userinterface receiving feedback of the touch control operations. The usersees the results on the display. Further interactions from the user canbe processed by repeating steps from S8 to S22.

FIG. 10A illustrates a flowchart of tomographic touch sensor operation.In step 100A a tomogram representative of touch interactions over thesensitive surface of the panel is acquired from a tomograph, using as anexample the embodiment in FIG. 12. In step 100B the tomogram output ofstep 100A is made accessible as digital information used to control adigital device as a result of the touch interactions.

FIG. 10B illustrates a flow chart of tomographic touch screen operationin which step 105A acquires, when needed, a tomogram representative oftouch interactions over the sensitive surface from a tomograph andprovide it to a computer using possible embodiment in FIG. 12, and instep 105B access, when needed, image information generated by thecomputer, and display result, to be seen through the sensitive surfaceas feedback of touch interactions.

FIG. 11 is a flow chart of an Interactive system using a tomographictouch sensor, a data processing element, and an output device. In step110A a data processor accesses the tomogram representative of touchinteractions produced by a user over the sensitive surface. In step 110Bthe tomogram is processed with DSP algorithms. In step 110C a decisionis taken whether it is an events-based interactive system? If YES, theprogram advances to step 110D where touch interactions from the tomogramare recognized and touch events are generated. In step 110F, the touchevents in step 100D are received and a user-interface software programrunning in the data processor modifies is state in response to the touchevents. If NO, the program advances to step 110E where a user-interfacesoftware program running in the data processor transforms the tomogramand modifies its state. The output of steps 110E and 100F feed to step110G where the user interface software provides informationrepresentative of its modified state to the output device as feedback ofthe touch interactions.

FIG. 12 is a flow chart showing an example embodiment for theacquisition of a tomogram representative of touch interactions. In step120A, parameters are defined for tomogram acquisition, includingemission pattern sequence, set of detector ports associated with eachemission pattern, and amount, position and shape of each reconstructionregion, using possible embodiment in FIG. 15. In step 120B anunreconstructed tomogram representative of the touch interactions overthe sensitive surface is acquired by estimating and measuring the portsaround the sensitive surface, using possible embodiment in FIG. 13. Instep 120C the reconstructed tomogram is calculated by transforming theunreconstructed tomogram with a tomographic reconstruction algorithm,using possible embodiment in FIG. 14.

FIG. 13 is a flow chart illustrating an example embodiment for theacquisition of an unreconstructed tomogram representative of touchinteractions. In step 130A configure a pattern controller with anemission pattern selected in turns from the set of defined emissionpatterns to energize emitter ports. In step 130B access through a signalsampler, to the measurement values from the set of detector portsassociated with the selected emission pattern. In step 130C append themeasurement values to the partially acquired unreconstructed tomogram.The output is put to a decision in step 130D regarding is any pattern ofthe set of defined emission patterns not yet applied to have completethe unreconstructed tomogram acquisition? If YES, then the program jumpsor loops back to step 130A; if NO, the program outputs.

FIG. 14 illustrates a flowchart for an example embodiment for thereconstructed tomogram calculation. In step 140A the system providesmatrix A, obtains its pseudoinverse A′ by truncated SVD. In step 140Bthe unreconstructed tomogram is optionally preprocessed. In step 140Cx=A′b is calculated, where x is the reconstructed tomogram and b is theunreconstructed tomogram. In step 140D the unreconstructed tomogram isoptionally post-processed.

FIG. 15 illustrates a flowchart of an example embodiment for thedefinition of parameters for tomogram acquisition. In step 150A theamount, positions, and shapes of imaginary or notional reconstructionregions on the sensitive surface are defined. In step 150B amount ofemission ports to be involved in unreconstructed tomogram acquisition isdefined, and positions selected. In step 150C a linearly independent setof emission patterns is defined. In step 150D amount of detector portsto be involved in unreconstructed tomogram acquisition is defined, andpositions selected. In step 150E for each emission pattern a set ofassociated detector ports is defined. In step 150F the system matrix Ais calculated assuming a linear model of the tomographic system. Theoutput of step 150F is passed to a decision in step 150G, namely, is therank and condition number of the system matrix A enough to allow anadequate posterior reconstruction? If the answer is YES, the signal isoutput; if the answer is NO, the signal is looped back to step 150A.

The best mode contemplated for practicing the present invention, as ofthe filing of this application, is an interactive system with theoptical FTIR-based embodiment. This embodiment permits the use of apanel with almost perfect light transmission properties, the detectionof touch interactions with zero-pressure and also with above-zeropressure, and the use of a very low-cost panel, and other manufacturingadvantages, like ease of mounting. This embodiment is detailed asfollows.

A conventional LCD display is used as an output device. On top of thedisplay, there's a clear panel made of a sheet of acrylic of less than afew millimeters thick, where infrared light passes from the borders. Theobjective is to make the screen visible through the panel. The panel isin mechanic contact with the screen by using two-sided tape put on theborders of the screen top, out of its active visible area. To preventthe display making unwanted TIR effect frustration on the panel's bottomsurface, the tape is reflective or mirror-like. The tape is thick so ifmechanic deformation occurs when pressure is applied with the fingers,the panel doesn't touch the screen. The panel shape is similar to arectangle, but octagonal with short diagonal corners similar to thepanel shown on FIG. 5A. The panel borders are unpolished so to preventtotal reflections on the borders and also to provide some diffusion whenlight enters or exits the panel's border.

Surrounding all panel perimeter, there are infrared LEDs used asemitters and photo transistors used as detectors, touching the panel'borders, so infrared light can enter and exit from the panel. The LEDand photo transistors are alternating, each emitter between twodetectors and vice versa. The emitters and detectors are spaced apart atregular intervals on each panel edge, separated by about one millimeter.The emitters and detectors are soldered on different Printed CircuitBoards, one for each panel edge.

The emitters are connected to a circuit that works similar to a LEDMatrix controller that permits to activate any LED. The possibleactivation levels for each LED are two: no current or the maximumcurrent allowed for the emitters. Taking into account each LED is activejust a short period of time, more than the nominal continuum rate ofemission is possible, like in conventional LED Matrices.

The photo transistor detectors have infrared filters matching theemission spectrum of emitters. Each phototransistor makes its currentflow through a resistance to convert the current in voltage. Thedetectors are grouped in groups of eight elements, and each groupconnected to an 8-to-1 analog multiplexer.

Each analog multiplexer is associated with a 14-bit Analog to DigitalConverter, and each digital output of the ADCs are connected to adigital multiplexer, so each ADC conversion value can be addressed. Thedigital multiplexer is a bus-based one, so each non-selected ADC is inhigh impedance state while the addressed one ADC is in low impedancewith respect to the bus.

The LED matrix controller and the digital multiplexer are connected to aFPGA that controls them and is able to execute a TomographicReconstruction Algorithm.

The FPGA is connected to a CPU adapted to be able to run an applicationwith a User Interface. The CPU is also connected to the display.

On the panel's top surface a pixilated matrix is defined. The total areamatches the screen's visible area. The pixels are square with a sidesize matching emitter and detectors separations. A vector representingan unreconstructed tomogram is acquired by energizing in turn eachemitter, and while each emitter is active, taking a measurement from alldetectors. To optimize acquisition time, all ADC are commanded inparallel to take the measurement using a selected multiplexer channel,repeating this for the eight acquisition channels. The measurements aresent to the FPGA through the bus.

Each time an emitter is energized and measurements are taken, anotherset of measurements is taken but with all emitters deactivated. Thismeasurement is to read ambient light interference level to be subtractedfrom the measurement with the emission pattern active. That measurementis taken many times because ambient light can be varying, for examplemost light bulbs oscillates at 120 Hz. To estimate the interferencelevel at the time of measurement with the emitter active, an averagewith previous and past interference measurement is calculated. Thistakes into account the fact that photo transistors are not as fast asother optoelectronic devices like PIN photo diodes, so beforemeasurement a delay is inserted to account for phototransistor timeresponse.

With the tomogram acquisition as described, a base measurementrepresentative of the tomogram acquired when no touch interactionsoccurs, is taken at factory and stored with the device on a providedmemory. That base measurement is called b0. This measurement is taken inevery touch device produced, to account possible variations on eachspecific device properties. For example, not all LED in a batch producesthe same level of light emission for same conditions. So thismeasurement accounts for that possible variation.

A linear model of the tomographic system is assumed. The system matrix Ais also calculated at factory by methods used to achieve AlgebraicReconstruction Methods. Each column of matrix A is the unreconstructedtomogram taken when a determinate “unity” touch interaction is ineffect. This unreconstructed tomogram is the change with respect to thebase tomogram b0. The “unity” touch interaction is an interaction in adeterminate region with a shape and position in accordance with thatregion. Columns of matrix A are representing each reconstruction region.Each “unity” touch interaction can be made by actually touching thepanel with a mechanic arm, or by simulating the effect. Those skilled inthe art will know to simulate the effect but a method is proposedanyways. Since the rows of system matrix A represents a determinate pairof emitter-detector, for each emitter-detector pair, the row representsall regions associated with that pair. The regions correspond to apixilated grid and each region has an associated coefficient, so it canbe viewed like a 2D grayscale image canvas. To calculate eachcoefficient, an anti aliased “white” line is drawn between the emitterand detector on a “black” background, taking into account emitter anddetector coordinates. White corresponds to value 1 and black to 0. The“gray” level of each canvas pixel is then associated with the rowcoefficient. Then each row coefficient is multiplied with the value ofthe corresponding pair from base tomogram b0, to account for actualsignal levels involved on the specific device implementation. Arectangular system matrix A is used with more columns that rows, so moremeasurements are taken than the amount of regions. More measurementsthan regions are useful to have more precision on tomographicreconstruction. It should be noted that on all steps for tomographicreconstruction, information associated with some pairs ofemitter-detector are not taken into account. Some are discardedaccording to the following criteria: if the dot product of correspondingrow on A matrix is below a threshold. The threshold is selected in a waythat the rank of A matrix isn't much below region count.

Having the system matrix A, a pseudoinverse A′ is calculated by theTruncated SVD method, by using MATLAB's pinv function. The toleranceparameter is calculated as follows. A value, say 1, is selected. Then bycomputer simulation, the reconstruction noise for a set of simulatedtouch interactions is calculated. Based on the noise properties ofsimulation results for each region, the value is lowered or incremented,so an optimization algorithm is run. The objective is to have noiselowered and if possible equally distributed for all the regions. Apractical value is sometimes around 0.4. The pseudoinverse A′ is alsostored on device for later recall.

Once all parameters for tomographic reconstruction are calculated, thedevice enters an interactive loop that runs continuously.

A tomogram b is acquired as described, with the base tomogram b0subtracted, so if no touch interactions are occurring, the b vectorcontains zeros or just normal noise values. A reconstructed tomogram xis calculated by solving the equation x=A′b on the FPGA, by techniqueswell know to those skilled in the art. The reconstructed tomogram, asrepresented by vector x, is interpreted as an image representing touchinteractions, with each pixel corresponding to each reconstructionregion.

The tomogram x is transmitted to the CPU, where it is post processed bya noise gate, thus making zero the values below some threshold. Thethreshold is by default fixed just above normal reconstruction noise.The default threshold value is also calculated at factory but a noisecontrol knob is provided to the user that can run configurationsoftware.

On the CPU, a set of current and previous tomograms are analyzed to findtouch events and gestures. The software used analyzes the events byexecuting a Blob Detection and Tracking algorithm. The algorithm can beselected by the user with a configuration application, where adaptedversions of the software TOUCHLIB, http://www.nuigroup.com/touchlib/ andOPENTOUCH, http://code.google.com/p/opentouch/ are offered as options.

After events or gestures are recognized, they are sent by TUIO protocolto applications adapted to work with that protocol. An exampleapplication is a GPS mapping application.

The application running on the CPU generates visual information asfeedback that is sent to the display to be seen through the panel by theuser, thus being that visual response feedback of the control operationsintroduced by touching the touch device of the present invention.

Although the present invention has been described regarding severalillustrative embodiments, numerous variations and modifications will beapparent to those skilled in the art that do not depart from theteachings herein. Such variations and modifications are deemed to fallwithin the purview of the appended claims.

What is claimed is:
 1. A touch sensitive human-computer interactiondevice comprising: a waveguide having a touch surface; a plurality oflight emitters optically coupled at input locations around the peripheryof the waveguide touch surface to emit light signals for transmissionthrough the waveguide by the internal reflection effect, wherein one ormore touch interactions on the touch surface of the waveguide alters thelight conductivity of the waveguide in the location(s) of the one ormore touch interactions causing frustration of the internal reflectioneffect; a plurality of detectors optically coupled at output locationsaround the periphery of the waveguide touch surface to receive the lightsignals along respective sensing signal paths defined between eachrespective pair of light emitter and detector, and arranged with adevice comprising an analog to digital converter to output respectivesignals on the basis of the light signals received; wherein each outputsignal is representative of the level of frustration of the internalreflection caused by one or more touch interactions along the respectivesensing signal paths, and wherein each output signal is alterable byeach of a plurality of simultaneous touch interactions along a singlesensing signal path of the respective signal paths; and a data processoroperatively coupled to the device comprising the analog to digitalconverter and arranged to process said output signals according to areconstruction algorithm to obtain a digital representation of saidlight conductivity and, based on the reconstruction, to output a signalfor controlling a visualization device, wherein the reconstructionalgorithm is a Computerized Tomography reconstruction algorithm.
 2. Thetouch sensitive human-computer interaction device according to claim 1,wherein the level of each said output signals is further alterableaccording to the level of pressure of each touch interaction and saidreconstruction accordingly represents said respective pressure levels.3. The touch sensitive human-computer interaction device according toclaim 1, wherein said processing further discriminates interiorproperties of the one or more touch interactions.
 4. The touch sensitivehuman-computer interaction device according to claim 1, wherein saidprocessing further discriminates the light conductivity at a pluralityof contact areas defined on the touch surface.
 5. The touch sensitivehuman-computer interaction device according to claim 1, wherein saidComputerized Tomography reconstruction algorithm is implementedaccording to the Projection-Slice theorem.
 6. The touch sensitivehuman-computer interaction device according to claim 1, wherein saidprocessing further provides location information of the one or moretouch interactions relative to the touch surface.
 7. The touch sensitivehuman-computer interaction device according to claim 1, furtherincluding the visualization device, wherein the waveguide is transparentand the visualization device is located on the opposite side of thewaveguide to the touch surface.
 8. The touch sensitive human-computerinteraction device according to claim 1, wherein the waveguide iscurved.
 9. The touch sensitive human-computer interaction deviceaccording to claim 1, wherein the waveguide is flexible.
 10. The touchsensitive human-computer interaction device according to claim 1,wherein said signal paths collectively define more than two angles. 11.The touch sensitive human-computer interaction device according to claim1, further comprising a plurality of analog to digital converters. 12.The touch sensitive human-computer interaction device according to claim11, wherein the plurality of analog to digital converters operate inparallel.
 13. A method of controlling a visualization device using atouch sensitive human-computer interaction device comprising: awaveguide having a touch surface; a plurality of light emittersoptically coupled at input locations around the periphery of thewaveguide touch surface to emit light signals for transmission throughthe waveguide by the internal reflection effect, wherein one or moretouch interactions on the touch surface of the waveguide alters thelight conductivity of the waveguide in the location(s) of the one ormore touch interactions causing frustration of the internal reflectioneffect; a plurality of detectors optically coupled at output locationsaround the periphery of the waveguide touch surface to receive the lightsignals along respective sensing signal paths defined between eachrespective pair of light emitter and detector, and arranged with adevice comprising an analog to digital converter to output respectivesignals on the basis of the light signals received; wherein each outputsignal is representative of the level of frustration of the internalreflection caused by one or more touch interactions along the respectivesensing signal paths, and wherein each output signal is alterable byeach of a plurality of simultaneous touch interactions along a singlesensing signal path of the respective signal paths; and a data processoroperatively coupled to the device comprising the analog to digitalconverter; wherein the method includes the steps of the data processor:processing said output signals according to a reconstruction algorithmto obtain a digital representation of said light conductivity and,outputting, based on the reconstruction, a signal for controlling thevisualization device, wherein the reconstruction algorithm is aComputerized Tomography reconstruction algorithm.
 14. The methodaccording to claim 13, wherein the level of each said output signals isfurther alterable according to the level of pressure of each touchinteraction and said reconstruction accordingly represents saidrespective pressure levels.
 15. The method according to claim 13,wherein said processing further discriminates the light conductivity ata plurality of contact areas defined on the touch surface.
 16. Themethod according to claim 13, wherein said processing further provideslocation information of the one or more touch interactions relative tothe touch surface.
 17. The method according to claim 13, wherein thetouch sensitive human-computer interaction device includes thevisualization device, and the waveguide is transparent and thevisualization device is located on the opposite side of the waveguide tothe touch surface.
 18. The method according to claim 13, wherein saidsignal paths collectively define more than two angles.
 19. The methodaccording to claim 13, further comprising a plurality of analog todigital converters.